1. Field of the Invention
The present invention relates to a transceiver apparatus, and more particularly to a transceiver apparatus in which a transmitter circuit and a receiver circuit for processing transmitted and received signals respectively are balanced circuits.
2. Description of the Related Art
Transceiver apparatuses often employ a constitution in which the transmitter and receiver circuit sections thereof are balanced circuits. Such a constitution makes it possible to use differentiation to cancel out internal digital noise and the like which is superposed on transmitted and received signals, thereby permitting an improvement in the accuracy of the transmission and reception operations.
A representative constitution of a conventional high frequency signal transceiver apparatus in which the transmitter and receiver circuit sections thereof are balanced circuits is shown in FIG. 3. The conventional high frequency signal transceiver apparatus comprises an antenna 1 for transmitting and receiving digitally modulated high frequency signals, a band pass filter 2 for limiting the transmitted and received signals of the antenna 1 to a predetermined frequency band, a switch circuit 3 for allowing the antenna 1 to be shared by the transmitter and receiver systems; a receiver circuit section 4 and a transmitter circuit section 5 which are connected to the switch circuit 3; and a local oscillator 6 for generating a local signal required in the frequency conversion processing by the circuits 4 and 5.
The receiver circuit section 4, the transmitter circuit section 5 and the local oscillator 6 are mounted in the same semiconductor chip (not shown) in a semiconductor integrated circuit device 9. Further, the semiconductor integrated circuit device 9 comprises a package frame (terminals 91 to 94), part of which protrudes outside the package. The package frame (terminals 91 to 94) is connected within the package to the receiver circuit section 4 or the transmitter circuit section 5 via bonding wire (not shown). The terminals 91 and 92 are terminals for connecting the receiver circuit section 4 to an external component (the switch circuit 3), and the terminals 93 and 94 are terminals for connecting the transmitter circuit section 5 to an external component (the switch circuit 3).
The switch circuit 3 selects either one of the receiver circuit section 4 and the transmitter circuit section 5 to render a state in which the circuit selected and the band pass filter 2 are connected.
The receiver circuit section 4 comprises a low noise amplifier 41 for amplifying the output signal of the switch circuit 3; an image rejection mixer 42 for generating an intermediate frequency signal by mixing the output signal of the low noise amplifier 41 and the local signal of the local oscillator 6, and for removing an image signal from this intermediate frequency signal; a band pass filter 43 for limiting the output signal of the image rejection mixer 42 to within a predetermined frequency band; a limiter amplifier 44 for amplifying the output signal of the band pass filter 43; a demodulator 45 for carrying out demodulation processing on the output signal of the limiter amplifier 44; and a slicer 46 for waveform shaping the output signal of the demodulator 45 and then outputting this signal to an internal circuit (not shown).
On the other hand, the transmitter circuit section 5 comprises an I/Q quadrature modulator 51 for quadrature-modulating the local signal of the local oscillator 6 on the basis of an I signal, an I bar signal, a Q signal and a Q bar signal which are inputted by an internal circuit (not shown); and a variable gain power amplifier 52 for amplifying the output signal of the I/Q quadrature modulator 51 and then transmitting same to the switch circuit 3.
As can be seen from FIG. 3, the antenna 1 and the band pass filter 2 are an unbalanced circuit, and the receiver circuit section 4 and the transmitter circuit section 5 are balanced circuits. A transformer circuit (referred to as a balun hereinafter) must be provided between the unbalanced circuit and the balanced circuits. Consequently, in the conventional high frequency signal transceiver apparatus shown in FIG. 3, a balun function is also added to the switch circuit 3.
The balun must be provided with inductors having a large inductance value, and it is therefore big and difficult to install the balun in the semiconductor integrated circuit device. Consequently, the switch circuit 3 provided with the balun function is an external component rather than being installed in the semiconductor integrated circuit device 9. With a conventional transceiver apparatus, when the transmitter and receiver circuit sections are balanced circuits, the balun is therefore made an external component, which has precluded miniaturization.
Furthermore, the conventional high frequency signal transceiver apparatus shown in FIG. 3 is constituted such that the terminals which connect the receiver circuit section 4 to an external component, and the terminals which connect the transmitter circuit section 5 to an external component are not shared, meaning that the number of terminals provided in the semiconductor integrated circuit device 9 is high, which has made miniaturization impossible.